Gas Hydrate Occurrence Research Articles

Gas Hydrate Saturation Estimates, Gas Hydrate Occurrence, and Reservoir Characteristics Based on Well Log Data from the Hydrate-01 Stratigraphic Test Well, Alaska North Slope

The Hydrate-01 Stratigraphic Test Well was drilled at the Kuparuk 7-11-12 site on the Alaska North Slope in December 2018. Sonic log data provide compressional (P) and shear (S) slowness from which we determine gas hydrate saturation (Sgh) estimates using effective medium theory. The sonic Sgh estimates compare favorably with Sgh estimated from resistivity and nuclear magnetic resonance (NMR) logs, showing that gas hydrate occupies up to approximately 90% of the pore space in the target reservoir sands. The informally named B1 sand (2294 feet below mean sea level) shows lower VP/VS ratios than the D1 sand (2770 feet below mean sea level), with the lower part of the B1 sand showing lower VP/VS ratios than the upper part of the B1 sand. This corresponds to a stiffer, or more “cemented”, behavior for the lower B1 sand and less cemented behavior for the D1 sand. This trend could be due to differences in the reservoirs themselves or in the gas hydrate morphology or to both factors. We observe that the presence of gas hydrate in the upper B1 sand has greater impact on hydraulic permeability (measurements suggest a greater difference between intrinsic and effective permeability) than in the D1 sand, possibly related to gas hydrate morphology but more likely due simply to higher gas hydrate saturations in the upper B1 sand. Analyses of Sgh relative to porosity, shale fraction, and intrinsic permeability show that reservoir quality (as represented by these three metrics) exerts control on gas hydrate saturation. Grain size and mineralogy data show somewhat smaller grains and better sorting in the D1 reservoir relative to the upper B1 reservoir and smaller grains and greater clay fraction in the lower B1 reservoir relative to the other two reservoir zones. Together, these data suggest that reservoir characteristics play a role in the observed VP/VS patterns, but gas hydrate morphology (possibly varying with saturation) must also be considered.

Numerical prediction of phase equilibrium conditions of gas hydrates up to 200 MPa in the presence of sodium and calcium chloride solutions

The occurrence of natural gas hydrates has both beneficial and negative practical implications. Nowadays, the most numerical studies in gas hydrates formation field were limited to a pressure of 74 MPa. However, these components are abundantly formed at permafrost and under the seafloor in which the pressure exceeds 100 MPa. In this study, the prediction of equilibrium conditions of gas hydrates was investigated numerically in pure gas and gas mixture up to 200 MPa. The inhibition of hydrates formation was examined by using NaCl and CaCl2 at different molar fractions. The Lee-Kesler-Plocker equation of state was selected as the most adequate, to predict gas hydrate stability limits, compared to other numerical approaches. The modeling results indicate that our model is in good agreement with experimental findings up to 200 MPa, but due to the lack of data in literature the maximum pressure compared was 163.25 MPa for gas mixture in pure water. The salt inhibition investigation also shows a good accuracy of our model at molar fractions less than 0.05 in both pure gas and gas mixture. It can be concluded that this model permits to study the stability limits of hydrates in wide range of gas composition and chloride salt solutions.

Hydrate formation and dissociation characteristics in clayey silt sediment

The geological occurrence of natural gas hydrates in clayey silt sediments has been extensively confirmed. Compared with sandy sediments, clayey silt is characterized by a large specific surface area, high capillary pressure, and high bound water content, which leads to distinct characteristics of hydrate formation and dissociation. The formation and dissociation of methane hydrates in clayey silt sediments with illite or montmorillonite were experimentally investigated. It was determined that an increase in the water content of silt and illite-silt sediments from ~9.47% to ~28.41% caused a decrease in the water-to-hydrate conversion ratio owing to the formation of a hydrate film between water and CH4 gas. However, in montmorillonite-silt sediments, the water-to-hydrate conversion rate increased between 9.47% and 18.94% of water saturation and decreased between 18.94% and 28.41% of water saturation under the combined effects of weakly bound water content and capillary pressure. In the hydrate dissociation experiment, the temperature of sediments with ~9.47% water content decreased more, which was caused by the smaller specific heat capacity of sediments with lower water content. Meanwhile, the temperature drops below the freezing point during the hydrate dissociation process, which is caused by the strong inhibition of hydrate phase equilibrium by montmorillonite. This study demonstrates the effects of clay type and water content on hydrate formation and dissociation, which is helpful for understanding the production behavior of clayey silt hydrate reservoirs.

Gas hydrate stability zone in Muri coalfield, Qinghai Province, China

ABSTRACTThe gas hydrate stability zone (GHSZ) is the essential condition for gas hydrate accumulation, which is controlled by three main factors: gas component, geothermal gradient and permafrost thickness. Based on the gas component of hydrate samples from drilling in Muri coalfield, the gas hydrate phase equilibrium curve was calculated using Sloan's natural gas hydrate phase equilibrium procedure (CSMHYD) program. Through temperature data processing of coalfield boreholes, some important data such as thickness of permafrost and geothermal gradient were obtained. The GHSZ parameters of a single borehole were calculated by programming based on the above basic data. The average thickness of GHSZ of 85 boreholes in Muri coalfield amounted to approximately 1000 m, indicating very broad space for gas hydrate occurrence. The isogram of GHSZ bottom depth drawn from single borehole data in Muri coalfield demonstrated the regional distribution characteristics of GHSZ, and identified three favourable areas of gas hydrate occurrence where the bottom of GHSZ had a burial depth >1500 m – namely, the southern part of Juhugeng Mining Area, the middle part of Duosuogongma Mining Area and the eastern part of Xuehuoli Mining Area.

Submarine landsliding in carbonate ooze along low-angle slopes (Inner Sea, Maldives)

Multichannel seismic and hydroacoustic data from the Maldives carbonate platform in the northern Indian Ocean document 4–8 km wide and are 70–170 m thick submarine landslides at water depths greater than 500 m, potentially associated with extensive fluid escape and the occurrence of gas hydrates. The mobilized sediments are part of giant drift bodies that consist of fine-grained carbonate ooze. Their downslope extent is located adjacent to large gateways that connect the semi-enclosed inner basin of the carbonate platform with the open Indian Ocean. Exposed at the sea-floor are headwall and translational domain of the landslides, showing different kinematic indicators typical for mass transport complexes. The submarine landslides evolved at slightly inclined slopes (<1°) along a listric basal shear surface (BSS) by downslope progradation and retrogressive failure. Styles of motion include sediment creeping, sliding and slumping. Where the BSS is flat, sediments translate as a large body. Where the BSS is irregular, folded, thrusted and rotated blocks/ridges occur, associated with secondary listric shear faults. Characteristically for the headwall domain are arcuate depressions which are related to rollover structures in the displaced slide block. The distal toe domain of the submarine landslides is located at the steep (>20°) part of the platform slope which faces the Indian Ocean. Data show that landslide activity is ongoing.The likely trigger of slope failure is a combination of gravitational forces and the reduction of sediment shear strength moderated by fluid ascent and the destabilization of gas hydrates. Gas hydrates are suggested to play an important rule, because the top of the gas hydrate stability zone coincides with a significant steepening of the platform slope from 1-3° to 10–20°. It is therefore proposed that the dissociation of the gas hydrates, for example during sealevel lowstands might have been an additional trigger of slope failure. During sealevel highstands, gas-hydrate coating of sediment grains may facilitate low-velocity plastic deformation of the strata.

Gas hydrate formation beneath thrust ridges: A test of concepts using 3D modelling at the southern Hikurangi Margin, New Zealand

Gas hydrates are widespread along convergent margins, but their distribution is highly variable. This variability has been attributed to a range of factors, such as the source of gas and the occurrence of permeable faults and porous or fractured reservoirs. We test these concepts on the Hikurangi Margin, where gas hydrate occurrences of variable character are well-documented by seismic reflection datasets and scientific drilling. We use 3D gas hydrate systems modelling to reconstruct processes of gas generation, migration and gas hydrate formation through time in two thrust ridges at the deformation front (Glendhu and Honeycomb ridges). We compare the results of scenarios using different fault and rock properties with indications for concentrated gas hydrates in reflection seismic data. Gas hydrate distributions are best reproduced by models predicting focussed gas migration through thrust faults and permeable strata. The gas is predominantly sourced from microbial generation beneath the gas hydrate stability zone (HSZ) in sedimentary troughs adjacent to the ridges and migrates up-dip as free gas. During progressive ridge deformation, gas generation shifts to the landward side of the ridges, where strata are rapidly buried, while erosion occurs at the crest of the ridges. A prominent back-thrust in the structurally more mature Glendhu Ridge diverts migrating gas into the HSZ and leads to preferential gas hydrate formation in the landward side of the ridge. Recycling of gas at the base of the HSZ during the past 2 Myrs led to an enrichment of gas hydrates, first in the center of the anticlines and then progressively more in the landward limbs. We propose that this process of diverting gas migration into the HSZ during thrust ridge formation is a common feature not only at the southern Hikurangi Margin, but in many convergent margins with high sedimentation rates and a thick accretionary wedge.

Influence of seafloor topography on gas hydrate occurrence across a submarine canyon-incised continental slope in the northern margin of the south china sea

In a submarine canyon-incised continental slope, the observed bottom simulation reflection (BSR) frequently appears not to match with the predicted base of the gas hydrate stability zone (BGHSZ). However, the mechanism behind this discrepancy is often debated due to the lack of in-situ borehole measurements. In the Shenhu area, a submarine canyon region on the northern continental slope of the South China Sea, a suite of datasets, including 3D seismic data, well logs and in-situ borehole temperature measurements enable us to study the gas hydrate stability zone. In-situ borehole temperature measurements reveal a nonlinear geothermal gradient within shallow 200 m-thick marine sediments. The geothermal gradient fit with the uppermost sediment interval (<50 m) neglected produces a better match between the depths of predicted BGHSZ and observed BSR. The gas hydrate stability zone (GHSZ) modeling using in-situ borehole measurement information at Site W07 shows that the predicted BGHSZ agrees well with the imaged BSR located atop an inter-canyon ridge, demonstrating that the gas hydrate system is in a steady state. Two-dimensional GHSZ modeling along seismic profiles transecting the ridge shows that the observed BSRs along the western margin of the ridge are deeper than the predicted BGHSZ. We interpret this apparent discrepancy to be attributed to topographic effects. Two scales of topographic effects, i.e. an alternating distribution of canyons and inter-canyon ridges, and localized crests and troughs over the crest of inter-canyon ridges, are revealed to influence gas hydrate system in the study area. The curved BGHSZ resulted from the topographic effect could facilitate the concentration of gas hydrate by enlarging the accumulation space and sealing free gas immediately below BGHSZ.

Reservoir characteristics and critical influencing factors on gas hydrate accumulations in the Shenhu area, South China Sea

The Shenhu area is the key target area for marine gas hydrate industrialization in China. Significant progress has been made with respect to gas hydrate exploration and production in this area in recent years. However, a comprehensive understanding of the reservoir characteristics and hydrate accumulation mechanism are still lacking; in particular, the hydrate enrichment factors are not, as yet, completely clear. In this study, we systemically characterize the geological controls on gas hydrate accumulation in the Shenhu area, including the sedimentary environment, gas sources, fluid and gas pathways, and reservoir-caprock system. We subsequently provide a quantitative evaluation of some critical factors influencing hydrate enrichment. The depositional environment in the study area was characterized by low energy (sedimentary hydrodynamic conditions), and anoxic environment, and the gas hydrate accumulations were closely associated with turbidites. The methane captured in the gas hydrates in the GMGS1 area and at the SHSC-4 and SHSC2-6 production test sites was mainly derived from the microbial reduction of CO2, while thermogenic gas was a more important source of hydrocarbon gases in the GMGS3 and GMGS4 areas. In addition, we used a combination of 8-slice spiral X-ray computed tomography (CT) and micro-CT techniques for the first time for the in-situ investigations of the microfractures and foraminifera in the hydrate cores. The results indicate that microfractures and foraminiferal shells are crucial to the occurrence and accumulation of gas hydrates in fine-grained sediments of the Shenhu area. Interestingly, microfractures were found to be more developed in the hydrate layers where most sediment particles were relatively small in size. Hydrate saturation increased with i) a decrease in the specific surface area of sediment grain, ii) an increase in the median pore size, and iii) increased foraminifera abundance in the reservoir. Our findings could help locate high-saturation gas hydrate layers (‘sweet spot’) in fine-grained marine sediments of the Shenhu area, South China Sea.

Behaviors of CH4 hydrate formation in cold seeps with underlying gas plume

Gas hydrates could occur as outcrop resources overspreading on the seafloor, coexisting with bubbling gas in activated cold seeps. This involves a complicated process of hydrate nucleation and accumulation in the sedimentary matrices as well as in the bulk water with an underlying gas plume. In addition, the escaping methane gas could also be a major concern in terms of its greenhouse effect. Consequently, the behaviors of hydrate formation in the sediments with a successive gas flow to mimic the cold seeps were monitored through magnetic resonance imaging technique in this work. It was found that the initial hydrate nucleation could occur universally throughout the sedimentary matrices resulted from an enhanced gas–water contact upon the gas flow. Specially, the substantial heat released upon hydrate formation could even locally trigger dissociation of adjacent hydrates. A faster hydrate formation was observed under higher gas flow rates and formation pressures, consolidating the dominant role of a sufficient gas–water contact in the hydrate formation. Nevertheless, large amount of residual water could still remain till the very end of the formation process; the subsequent reaction would be significantly limited by the gas diffusion barrier effect of the existing hydrate shell. The findings could provide insights into the kinetic process of hydrate formation in the cold seeps and expand our knowledge on the diverse occurrence of gas hydrate under the sea.

Heat Flow Measurements at the Danube Deep-Sea Fan, Western Black Sea

Seafloor heat flow measurements are utilized to determine the geothermal regime of the Danube deep-sea fan in the western Black Sea and are presented in the larger context of regional gas hydrate occurrences. Heat flow data were collected across paleo-channels in water depths of 550–1460 m. Heat flow across levees ranges from 25 to 30 mW m−2 but is up to 65 mW m−2 on channel floors. Gravity coring reveals sediment layers typical of the western Black Sea, consisting of three late Pleistocene to Holocene units, notably red clay within the lowermost unit cored. Heat flow derived from the bottom-simulating reflector (BSR), assumed to represent the base of the gas hydrate stability zone (GHSZ), deviates from seafloor measurements. These discrepancies are linked either to fast sedimentation or slumping and associated variations in sediment physical properties. Topographic effects account of up to 50% of heat flow deviations from average values. Combined with climate-induced variations in seafloor temperature and sea-level since the last glacial maximum large uncertainties in the prediction of the base of the GHSZ remain. A regional representative heat flow value is ~30 mW m−2 for the study region but deviations from this value may be up to 100%.

Influence of Gas Supply Changes on the Formation Process of Complex Mixed Gas Hydrates.

Natural gas hydrate occurrences contain predominantly methane; however, there are increasing reports of complex mixed gas hydrates and coexisting hydrate phases. Changes in the feed gas composition due to the preferred incorporation of certain components into the hydrate phase and an inadequate gas supply is often assumed to be the cause of coexisting hydrate phases. This could also be the case for the gas hydrate system in Qilian Mountain permafrost (QMP), which is mainly controlled by pores and fractures with complex gas compositions. This study is dedicated to the experimental investigations on the formation process of mixed gas hydrates based on the reservoir conditions in QMP. Hydrates were synthesized from water and a gas mixture under different gas supply conditions to study the effects on the hydrate formation process. In situ Raman spectroscopic measurements and microscopic observations were applied to record changes in both gas and hydrate phase over the whole formation process. The results demonstrated the effects of gas flow on the composition of the resulting hydrate phase, indicating a competitive enclathration of guest molecules into the hydrate lattice depending on their properties. Another observation was that despite significant changes in the gas composition, no coexisting hydrate phases were formed.

In-situ borehole temperature measurements confirm dynamics of the gas hydrate stability zone at the upper Danube deep sea fan, Black Sea

Coring, geophysical logging, and in-situ temperature measurements were performed with the MARUM-MeBo200 seafloor rig to characterize gas hydrate occurrences in sediments of the Danube deep sea fan, off Romania, Black Sea. The new drilling data showed no evidence for significant gas hydrate saturations within the sediments but the presence of free gas at the depth of the bottom-simulating reflector (BSR). In-situ temperature and core-derived geochemical data suggest that the current base of the gas hydrate stability zone (BGHSZ) is ∼20 m shallower than the BSR. Investigation of the seismic data around the drill sites shows several locations where free gas previously trapped at a former BGHSZ migrated upwards forming a new reflection above the BSR. This shows that the gas hydrate system in the Danube deep sea fan is still responding to climate changes initiated at the end of the last glacial maximum.

Authigenic Greigite as an Indicator of Methane Diffusion in Gas Hydrate-Bearing Sediments of the Hikurangi Margin, New Zealand

Authigenic ferrimagnetic iron sulfides, essentially greigite (Fe3S4), are commonly found in gas hydrate-bearing marine sediments of active accretionary prisms. Greigite is a by-product, either intracellular or extracellular, of microbial activity, and therefore provides good indication of microbial processes which are closely related to the occurrence of gas hydrate. A high-resolution rock magnetic study was conducted at Site U1518 of International Ocean Discovery Program Expedition 375, located in the frontal accretionary wedge of the Hikurangi Margin, offshore New Zealand. Samples were collected throughout the entire recovered stratigraphic sequence, from the surface to ∼492 m below seafloor (mbsf) which includes the Pāpaku fault zone. This study aims to document the rock magnetic properties and the composition of the magnetic mineral assemblage at Site U1518. Based on downhole magnetic coercivity variations, the studied interval is divided into five consecutive zones. Most of the samples have high remanent coercivity (above 50 mT) and first-order reversal curves (FORC) diagrams typical of single-domain greigite. The top of the hanging wall has intervals that display a lower remanent coercivity, similar to lower coercivities measured on samples from the fault zone and footwall. The widespread distribution of greigite at Site U1518 is linked to methane diffusion and methane hydrate which is mainly disseminated within sediments. In three footwall gas hydrate-bearing intervals, investigated at higher resolution, an improved magnetic signal, especially a stronger FORC signature, is likely related to enhanced microbial activity which favors the formation and preservation of greigite. Our findings at the Hikurangi Margin show a close linkage between greigite, methane hydrate and microbial activity.

Comparison of logging-while-drilling and wireline logging data from gas hydrate-bearing deep-sea sediments, the Ulleung Basin, East Sea

Gas hydrate exploration was conducted using logging-while-drilling (LWD) and wireline logging (WLL) at two sites (UBGH2-6 and UBGH2-10) in the Ulleung Basin, East Sea (Sea of Japan). Coring for gas hydrate sampling was also conducted. Seismic profiles revealed that the upper layers at the logged sites (∼180 m at UBGH2-6 and ∼150 m at UBGH2-10) are dominated by turbidite/hemipelagic sediments, whereas the lower-lying sediments are characterised by thick mass transport deposits. Except in the gas hydrate-bearing interval (140–160 metres below the seafloor) of UBGH2-6, the WLL velocity and resistivity data are a little higher (∼100 m/s and ∼0.4 ohm-m, respectively) than those indicated by LWD. Conversely, the density and porosity do not show a consistent pattern for the two methods. Discrepancies between LWD and WLL can be caused by the methodology, borehole condition, and gas hydrate occurrence type. The high resistivity values (∼100 ohm-m) in the gas hydrate-bearing zone of UBGH2-6 are typical of inclined fracture-filling gas hydrate. In this case, the LWD resistivity may be overestimated as a result of the data acquisition principle. The relationships between the physical properties are significantly controlled by the presence of gas hydrate. Therefore, in fracture-filling gas hydrate-bearing sediments, the WLL resistivity data are more reasonable than the LWD resistivity data. Both methods have advantages and disadvantages in terms of data quality, efficiency, and resolution. Therefore, it is necessary to compare and interpret data measured using both methods to identify the physical properties of gas hydrate-bearing sediments.

A Monte Carlo Model of Gas-Liquid-Hydrate Three-phase Coexistence Constrained by Pore Geometry in Marine Sediments

Gas hydrates form at relatively high pressures in near-surface, organic-rich marine sediments, with the base of the hydrate stability field and the onset of partial gas saturation determined by temperature increases with depth. Because of pore-scale curvature and wetting effects, the transition between gas hydrate and free gas occurrence need not take place at a distinct depth or temperature boundary, but instead can be characterized by a zone of finite thickness in which methane gas bubbles and hydrate crystals coexist with the same aqueous solution. Previous treatments have idealized pores as spheres or cylinders, but real pores between sediment grains have irregular, largely convex walls that enable the highly curved surfaces of gas bubbles and/or hydrate crystals within a given pore to change with varying conditions. In partially hydrate-saturated sediments, for example, the gas–liquid surface energy perturbs the onset of gas–liquid equilibrium by an amount proportional to bubble-surface curvature, causing a commensurate change to the equilibrium methane solubility in the liquid phase. This solubility is also constrained by the curvature of coexisting hydrate crystals and hence the volume occupied by the hydrate phase. As a result, the thickness of the three-phase zone depends not only on the pore space geometry, but also on the saturation levels of the hydrate and gaseous phases. We evaluate local geometrical constraints in a synthetic 3D packing of spherical particles resembling real granular sediments, relate the changes in the relative proportions of the phases to the three-phase equilibrium conditions, and demonstrate how the boundaries of the three-phase zone at the base of the hydrate stability field are displaced as a function of pore size, while varying with saturation level. The predicted thickness of the three-phase zone varies from tens to hundreds of meters, is inversely dependent on host sediment grain size, and increases dramatically when pores near complete saturation with hydrate and gas, requiring that interfacial curvatures become large.

An insight into shallow gas hydrates in the Dongsha area, South China Sea

Previous studies of gas hydrate in the Dongsha area mainly focused on the deep-seated gas hydrates that have a high energy potential, but cared little about the shallow gas hydrates occurrences. Shallow gas hydrates have been confirmed by drill cores at three sites (GMGS2 08, GMGS2 09 and GMGS2 16) during the GMGS2 cruise, which occur as veins, blocky nodules or massive layers, at 8–30 m below the seafloor. Gas chimneys and faults observed on the seismic sections are the two main fluid migration pathways. The deep-seated gas hydrate and the shallow hydrate-bearing sediments are two main seals for the migrating gas. The occurrences of shallow gas hydrates are mainly controlled by the migration of fluid along shallow faults and the presence of deep-seated gas hydrates. Active gas leakage is taking place at a relatively high-flux state through the vent structures identified on the geophysical data at the seafloor, although without resulting in gas plumes easily detectable by acoustic methods. The presence of strong reflections on the high-resolution seismic profiles and dim or chaotic layers in the sub-bottom profiles are most likely good indicators of shallow gas hydrates in the Dongsha area. Active cold seeps, indicated by either gas plume or seepage vent, can also be used as indicators for neighboring shallow gas hydrates and the gas hydrate system that is highly dynamic in the Dongsha area.

Gas Hydrate System Offshore Chile

In recent decades, the Chilean margin has been extensively investigated to better characterize the complex geological setting through the geophysical data. The analysis of seismic lines allowed us to identify the occurrence of gas hydrates and free gas in many places along the margin and the change of the pore fluid due to the potential hydrate dissociation. The porosity reduction due to the hydrate presence is linked to the slope to identify the area more sensitive in case of natural phenomena or induced by human activities that could determine gas hydrate dissociations and/or leakage of the free gas trapped below the gas-hydrate stability zone. Clearly, the gas hydrate reservoir could be a strategic energy reserve for Chile. The steady-state modelling pointed out that the climate change could determine gas hydrate dissociation, triggering slope failure. This hypothesis is supported by the presence of high concentrations of gas hydrate in correspondence of important seafloor slope. The dissociation of gas hydrate could change the petrophysical characteristics of the subsoil triggering slopes, which already occurred in the past. Consequently, it is required to improve knowledge about the behavior of the gas hydrate system in a function of complex natural phenomena before the exploitation of this important resource.

Effects of protein macromolecules and metabolic small molecules on kinetics of methane hydrate formation in marine clay

Numerous efforts have been made to mimic the natural marine environments to understand the behavior of hydrate formation and accumulation in the sediments under seafloor. Yet it is found that the role of organic matters in the kinetics of hydrate formation is largely veiled, which should be much enriched as a result of the activities of the marine ecosystem. Therefore in this study, the kinetic effects of protein macromolecules and metabolic small molecules on CH4 hydrate formation were examined; the organic compounds were extracted from the samples gathered from the hydrate reservoir located in the South China Sea. A total of 2058 species classified into 10 types of protein macromolecules and metabolic molecules were identified. Low-field nuclear magnetic resonance technique was used to in-situ monitor the hydrate formation process. The results showed that the metabolic molecules could remarkably promote hydrate formation, with more water converted into hydrate within a shorter time. Proteins have been widely studied to inhibit hydrate formation; here it is for the first time confirmed that the proteins extracted from the natural samples drilled in the hydrate reservoir could act as kinetic inhibitor, lowering the possibility of hydrate nucleation. It was further indicated that hydrate formation majorly consumed the water in the macro pores; this was followed by a diffusion-limitation process with the hydrate shell acting as mass transfer barrier slowing down the water conversion. The water in the micropores was yet found to be very difficult to participate in the reaction, potentially resulting from the unavailable gas-water contact. The findings could provide insights into the kinetics of hydrate formation in the presence of organic matters abundant in natural sediments and expand the current understandings on the occurrence of natural gas hydrate under marine environments.

A review of the gas hydrate distribution offshore Chilean margin

In last decades, the Chilean margin has been extensively investigated to better characterize the complex geological setting through the acquisition of geophysical data and, in particular, seismic lines. The analysis of seismic lines allowed identifying the occurrence of gas hydrates and free gas in many places along the margin. Clearly, the gas hydrate reservoir could be a strategic energy reserve for Chile, but, on the other hand, the dissociated of gas hydrate due to climate change could be an issue to face. Moreover, this region is characterized by large and mega-scale earthquakes that may contribute to gas hydrate dissociation and consequent submarine slides triggering. In this context, Chilean margin should be considered a natural laboratory to study the hydrate system evolution.

Identification and analysis of bottom simulating reflectors in the Foz do Amazonas Basin, Northern Brazil

This work proposed an additional approach to investigate gas hydrate occurrences in the Foz do Amazonas Basin, in the Brazilian Equatorial Margin. The automatic comparison of seafloor seismic amplitudes with those from the Bottom Simulating Reflectors (BSR) was used to exhibit the reversal of signal polarities among the seafloor (positive) and the BSR (negative), reinforcing the identification of BSR in areas where its visualization was unclear. Additionally, we used the envelope attribute to highlight the BSR in the seismic section. Subsequently, we decomposed the seismic data into different frequency bands, applied a -90 degrees phase rotation to the data and recalculated the envelope attribute for each section decomposed in frequency bands. This technique improved visualization, allowing the identification of intervals where BSR were laterally discontinuous, revealing to be valuable for mapping the gas hydrate distribution in Foz do Amazonas Basin.